FYI:
The MB manuel for the W123 says that off a tooth will be 18 deg. Having been there and done that I can tell you that the chain can very easily be moved over one tooth by loosening the tensioner and bunching the chain along the top of the cam gear. You should clamp one end to keep track of where it started.
I had the chain off a tooth and drove it about 1200 miles. Have not pulled the head, but it may have bent one of the valves a bit. Can hear a little wind blowing into the intake when compressed air is blown into the cylinder.